Yes it's possible to run it in stand alone with XULRunner Rated 5 out of 5 stars

1) First download XULRunner and the XPi for XULGear
2) Extract xulrunner, change xulgear xpi extension to zip and extract to a XULGear Folder inside xulrunner main folder.
+xulrunner
--XULGear
---chrome (and all the xpi files and folders)
3) create a file application .ini in XULGear folder with the following lines:
[App]
Vendor=XULGear
Name=XULGear
Version=1.0
BuildID=20140210
ID=xulapp@xultest.org

[Gecko]
MinVersion=1.8
MaxVersion=200.*

4) WINDOWS: Create the file XULGear.bat in xulrunner folder with the following line:
xulrunner.exe XULGear\application.ini
LINUX: Create an SH file with ./xulrunner XULGear/application.ini

5) Change the file prefs.js inside the XULGear folder:
XULGear/defaults/preferences
replace the configuration to contain only the following line:
pref("toolkit.defaultChromeURI", "/content/xulgear.xul");

6) Create a shortcut to the .bat or .sh you created.

This user has 3 previous reviews of this add-on.

Rated 5 out of 5 stars

Is it possible to run this add-on in XULRunner?

Cannot Create Dialog element Rated 5 out of 5 stars

Cannot Create <dialog> element

Rated 5 out of 5 stars

Great timesaver for those who do not have time digging into XUL manuals for building simple GUI elements.

Rated 5 out of 5 stars

awesome

This review is for a previous version of the add-on (1.0.9). 

I like this but there is something wrong with it Rated 3 out of 5 stars

I have been looking everywhere for a program that will help me develop extensions for firefox, or standalone XULRunner applications. So far, this extension looks like the best option besides using a plain text editor. I like that there is a selection menu for so many items, and a menu for each item selected. It is very easy to set the attributes for the items in a XUL document when using this extension. This is nice :D I had to uninstall this extension though, because every time I use it my processor gets extremely hot and my laptop starts cooking anything underneath it (my um... lap). I don't know what's going on when I fire up this extension, but if it didn't give me blisters I'd use it all the time. :D

Thank you for your work :D I hope you continue developing this extension :D

This review is for a previous version of the add-on (1.0.9). 

Rated 5 out of 5 stars

Great Plug-in thanks for the hard work you spent on this!

This review is for a previous version of the add-on (1.0.7). 

Rated 5 out of 5 stars

A classic "Holy crap that's a great idea, why didn't I think of it!" extension. Very well done.

This review is for a previous version of the add-on (1.0.7). 

Rated 5 out of 5 stars

This is a great start. Has potential

This review is for a previous version of the add-on (1.0.6). 

Rated 3 out of 5 stars

Неплохое начало, попробовал создать tabbox с тремя Tab-ми...Пока сыровато. В итоге вернулся к XUL Explorer.

This review is for a previous version of the add-on (1.0.1).